1. Field of the Invention
The present invention relates to a zoom lens, an image pickup apparatus using the same, an image transmission apparatus, and an image transmission system.
2. Description of the Related Art
In video photography, photography is carried out while zooming and focusing. In a case of carrying out always the zooming and focusing, a weight of a lens governs a focusing speed. Moreover, as an overall length of the lens changes at the time of focusing, an overall optical system and an image pickup apparatus becomes large. Moreover, a movement of center of gravity being large, the balance is not stabilized easily. Therefore, a zoom lens in which, the focusing speed is increased by moving a comparatively smaller lens, without moving a lens (group) of a front portion, and which is made compact as a whole, has been proposed.
As an example of a zoom lens in which, a first lens group is let to be fixed, a zoom lens which includes in order from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, and in which, at the time of zooming from a wide angle end to a telephoto end, the first lens group is fixed, the second lens group is moved toward an image plane side, the third lens group is fixed, and the fourth lens group is moved, and furthermore, the focusing is carried out by moving the fourth lens group, has been proposed. (Japanese Patent Application Laid-open Publication Nos. Sho 62-178917, Sho 63-29718, and Sho 63-123009)
Furthermore, a zoom lens in which, a fifth lens group (fixed lens group) having a positive refractive power is added to an image side of the fourth lens group has also been proposed. (Japanese Patent Application Laid-open Publication No. Hei 3-154014, Hei 5-264902, Hei 6-27375, and Hei 7-151967).